Generally, a contactless power supply system is formed by a power supplying device, which includes a power transmission coil, and a power receiving device, which includes a power reception coil. The power supplying device generates high frequency current and sends the high frequency current to the power transmission coil to generate an alternating magnetic field at the power transmission coil. The power receiving device interlinks the alternating magnetic field generated by the power transmission coil of the power supplying device with the power reception coil, which faces the power transmission coil, so that the power reception coil generates an induced electromotive force. The power receiving device rectifies the induced electromotive force generated by the power reception coil to generate direct current (DC) voltage and supply the DC voltage to a load or DC/AC converts the DC voltage and supplies alternating current (AC) voltage to the load.
Patent document 1 describes an example of the contactless power supply system that adapts a single power supplying device to a plurality of power receiving devices that generate different output voltages. The power supplying device includes a control means that controls the output voltage of each power receiving device to be within a predetermined voltage range throughout a region including a load region subject to each power receiving device.
As a specific means, patent document 1 describes the use of a resonance capacitor together with the power reception coil in the power receiving device to stop and start the supply of high frequency current to the power transmission coil of the power supplying device and control the output voltage.
Patent document 2 describes another example of the contactless power supply system that arranges a contactless extension plug between the power supplying device and the power receiving device. The contactless extension plug is configured by a closed circuit in which a power reception coil and a power transmission coil are connected in series by a resonance capacitor. The power reception coil of the contactless plug is arranged to face a primary coil of the power supplying device, and the power transmission coil of the contactless plug is arranged to face a secondary coil of the power receiving device.
The contactless extension plug allows power to be supplied to the power receiving device, which is spaced apart from the power supplying device, in a contactless manner. Furthermore, the contactless extension plug may also be used as a contactless voltage conversion plug to be applicable to an electrical appliance having a different load voltage.
Patent Document 1: Japanese Patent No. 4135299
Patent Document 2: Japanese Patent No. 4258505